The present invention relates to a thermally conductive sheet used to release heat generated by semiconductor devices and various types of electronic parts which are heat emitting bodies and a method of manufacturing the same.
Thermally conductive sheets, thermally conductive grease, thermally conductive adhesives, phase change members having thermal conductivity and the like are inserted between heat emitting bodies mounted on circuit boards for conventional electronics and heat discharging bodies in order to release heat generated by the heat emitting bodies. Specific examples of heat emitting bodies include semiconductor devices and electronic parts. Specific examples of heat discharging bodies include heat sinks and cooling fans. In recent years, the power consumption and amount of heat emission of electronic parts have increased as the functions and performance of electronics have increased. In addition, the space within the housing of electronics for arranging members, such as circuit boards, has been becoming smaller as the scale and the thickness of electronics have been reduced. When heat accumulates in electronic parts, for example, the processing performance in the electronic parts decreases, it becomes easy for the electronic parts to be damaged, and the higher temperature is unpleasant for the user of the electronic device. Thus, it is necessary to avoid heat accumulation in heat emitting bodies, for example in electronic parts and the like, and cooling of heat emitting bodies has become an important goal. Therefore, excellent thermal conductivity is required for thermally conductive sheets and the like.
In addition, thermal diffusion sheets formed of graphite or a metal material, for example, are used in order to effectively diffuse heat generated by a heat emitting body within the limited space inside the housing. In particular, it is necessary to avoid local heat accumulation in mobile devices of which the scale and thickness are small and where the density of heat emission is high. Thus, a thermal diffusion sheet having excellent properties in terms of thermal diffusion has been required. In the case where a thermal diffusion sheet makes direct contact with a heat emitting body, the thermal diffusion sheet does not stick to the shape of the contour of the heat emitting body, due to the high rigidity of the graphite or metal material that forms the thermal diffusion sheet. Therefore, the thermal diffusion sheet cannot make sufficiently close contact with the heat emitting body, and thus, excellent properties in terms of thermal diffusion cannot be gained.
Japanese Laid-Open Patent Publication No. 2003-168882, Japanese Laid-Open Patent Publication No. 2005-57088 and Japanese Laid-Open Patent Publication No. 2004-243650 disclose thermally conductive sheets where a flexible thermally conductive polymer layer is layered on at least one side of a thermal diffusion layer formed of, for example, graphite, in order to gain excellent properties in terms of thermal diffusion. Various functions are required, in addition to the above described properties in terms of thermal diffusion, for thermally conductive sheets, depending on where they are used. However, the thermally conductive sheets described in the above described gazettes do not meet these requirements.